Power Battery Pack Cooling Apparatus

ABSTRACT

Using a simple structure to facilitate a flow path delivering coolant in an even and well-distributed manner, providing efficient and effective cooling for power battery packs in electric vehicles. The heat exchange apparatus is composed of an ray of cooling duct plates, with ducts for coolant to flow within, with front and back covers and their respective rubber sheets facilitating the changing of direction of the coolant, providing a pathway for the coolant to flow throughout the array. Individual cells of the battery pack will be fitted in the spaces between these ducts, connected in series by a novel system of electricity-conducting clips, forming a structure where a comprehensive, well-distributed and compact cooling pathway can exist within the battery pack. The concept and structure of this power battery pack cooling apparatus can also apply to other future implementations and applications requiring compact and lightweight battery packs, or applications requiring effective cooling systems under space constraints.

INTRODUCTION

The supply of fossil fuels is slowly being exhausted, and burninggasoline is causing much environmental pollution. Electric vehicles(EVs) are the future of transportation, but their batteries have somecritical shortcomings: short range of vehicles, short service life, andhigh costs, preventing widespread consumer adoption. Regulating thebattery temperature during continuous charge and discharge is a majorchallenge.

For most Li-ion batteries used in EVs, their temperature specificationis normally as follows:

Operating temperature: −20° C. to 60° C.

Charging temperature: 0° C. to 45° C.

Storage temperature: −10° C. to 45° C.

They can achieve their rated capacity at 20˜25° C. and their capacitywill drop ˜10% for every increase of 10° C.

During winter, when temperatures can easily fall below 0° C., it will bedifficult or totally impossible for charging.

During other seasons, under continuous high current charge/discharge,the battery working temperature can easily reach 60° C., making itdifficult for discharging. Higher temperatures can also cause batterydegradation, shortened service life, or present safety hazards.

The specific characteristics of Li-ion cells require well-adapted andwell-designed battery temperature management and control systems.

In the subsequent paragraphs, for simplification, the word ‘cooling’will represent heat exchange, be it cooling or heating, and the word‘coolant’ will represent a liquid that has anti-freeze, non-flammable,non-corrosive and anti-fungal properties for heat exchange of thebattery cells, be it for cooling or heating.

Drawbacks of Existing Battery Packs

Present-day battery packs are constructed by connecting a number ofbattery modules, each module consisting of several cells connected sideby side. The result is that cells in the center of each module are morethermal insulated, resulting in more difficult heat exchange.

Existing battery cooling solutions normally consist of the batterymodules sitting on or attached to a heat sink (a flat metal plate) thatis cooled by a coolant loop. The drawbacks are that the coolingefficiency is low, and the effectiveness is poor, since only a smallpart of each module receives the cooling effect. Also, the heat sinksare generally thick and heavy due to the coolant loop. The result isthat temperatures will differ from module to module, cell to cell. Evenwithin the same cell, different regions may have different temperatures.If heat sinks were to be used to cool each cell, it would result in abattery pack with impractical weight and volume.

Consistency and uniformity of each cell in a battery pack is veryimportant for its durability and effectiveness. Once the cells areproduced and assembled into battery packs, the only factor that is ableto affect its consistency and uniformity is the temperature of eachcell. Temperature changes can affect the cells' internal resistance, andchanges to internal resistance can in turn affect the rate oftemperature change. The existence of a temperature gradient betweencells will cause different rates of cell ageing, resulting in certaincells having shorter lifespans. With the failure of a single cell, theoperation of the entire battery pack is compromised as all cells areinterlinked to work together.

Battery packs used in EVs are constrained by space and weight, socooling systems for the battery packs must be compact and lightweight,yet meeting the power and energy capacity requirements.

A More Compact, Lightweight and Longer Lasting Power Battery PackSolution

Based on the above observations, I studied and worked out a uniquebattery pack cooling apparatus suitable for EV requirements. Althoughthe design below is intended for applications in an EV and is aproof-of-concept for realistic application in an EV, it does not andwill not limit or affect the claims about its novel concept, principles,and structure for other applications.

The following drawings form part of this description,

FIG. 1/31 is a large-format laminated battery cell (100 Ah, 3.7V);

FIG. 2/31 is a 2S-cell (2 battery cells connected in series);

FIG. 3/31 is a small clip;

FIG. 4/31 is a big clip;

FIG. 5/31 is an end clip;

FIG. 6/31 is a cooling duct plate;

FIG. 7/31 is a cooling duct end plate;

FIG. 8/31 is the cooling grid array;

FIG. 9/31 is a front rubber sheet;

FIG. 10/31 is a front cover;

FIG. 11/31 is a front cover with front rubber sheet;

FIG. 12/31 is a back rubber sheet;

FIG. 13/31 is a back cover;

FIG. 14/31 is a back cover with back rubber sheet;

FIG. 15/31 is a bottom plate;

FIG. 16/31 is a side plate;

FIG. 17/31 is an empty battery box;

FIG. 18/31 is a battery box with multiple 2S-cells;

FIG. 19/31 is a detail view-C of FIG. 18/31;

FIG. 20/31 is a detail view-D of FIG. 18/31;

FIG. 21/31 is a top cover;

FIG. 22/31 is a battery pack box;

FIG. 23/31 is flow direction diagram;

FIG. 24/31 is cooling grid array front view with front rubber sheet;

FIG. 25/31 is a detail view-A & C of FIG. 24/31;

FIG. 26/31 is cooling grid array back view with back rubber sheet;

FIG. 27/31 is a detail view-A of FIG. 26/31;

FIG. 28/31 is cooling grid array top view with front and back rubbersheet cut-out space;

FIG. 29/31 is a front view-B of FIG. 28/31 to show coolant flowdirection at front rubber sheet cut-out space;

FIG. 30/31 is a back view-C of FIG. 28/31 to show coolant flow directionat back rubber sheet cut-out space;

FIG. 31/31 is a detail view-D & E of FIG. 28/31 to show coolant flowdirection at bottom flow duct layer.

For the battery cell type and cell specifications, I have selectedlaminated cells. Compared to cylindrical cells, laminated cells havelower internal resistance and therefore lower heat generation uponcharging and discharging. Also, it has a higher energy/power density.Because of its flat geometry and higher exposed surface area, it iseasier for beat exchange to take place.

I have designed the battery pack to have 86 pieces of large-formatlaminated cells (100 Ah, 3.7V, as shown in FIG. 1/31). The battery cellsare connected by means of a novel clip system, outlined below, whichprovides for electrical connectivity under space constraints.

Two cells are connected face-to-face in series (FIG. 2/31), with one ofthe terminals connected to the opposite terminal of the other cell, by asmall clip (FIG. 3/31). This will be one 2S-cell. Both sides of the2S-cell will be in contact with the cooling duct plate (FIG. 18/31) forheat exchange.

2S-cells are connected in series, with the terminals of each 2S-cell inidentical orientation. A big clip (FIG. 4/31) connects the terminalsbetween each 2S-cell, straddling the cooling duct plate (detail-D ofFIG. 18/31), which is between the two 2S-cells once they are insertedinto place.

End clips (FIG. 5/31) are used at the positive terminal of the firstcell of the first 2S-cell (FIG. 20/31), and the negative terminal of thelast cell of the last 2S-cell, for connection to main power cables. Allclips are made of metallic materials with electrical conductivity.

This will achieve the voltage (320V) and energy capacity (32 kWh) forpurely electric driving for a range of 120-150 km (the range of 90% ofdaily urban commuters).

To lower the cost of the battery pack box, extruded aluminum alloyconstruction will be used for the box construction plates whereverpossible.

FIG. 6/31 depicts the cooling duct plate. The divided hollow flow ductsare for the coolant to pass through and for heat exchange to take placewith the 2S-cells.

Both ends of the cooling duct plates are inserted into the cooling ductend plates cut-out slot (FIG. 7/31), resulting in a flushed outsidesurface. Friction Stir Weld (FSW) will be used to make a leak-proofjoint, forming a homogenous and regular structure—the cooling gridarray, depicted in FIG. 8/31, consisting of multiple cooling duct platesarranged in a row and attached to cooling duct end plates. The coolingduct plate also supports the battery cell and keeps the battery cell inits position and maintains its shape.

The front rubber sheet (FIG. 9/31) will sit in the recess of the frontcover (FIG. 10/31). The final configuration, as viewed from the sidewhere the rubber sheet is, is shown in FIG. 11/31.

The back rubber sheet (FIG. 12/31) will sit in the recess of the backcover (FIG. 13/31). The final configuration, as viewed from the sidewhere the rubber sheet is, is shown in FIG. 14/31.

The cut-out patterns of the front and back rubber sheets are slightlydifferent. The front rubber sheet has narrow cut-outs on its left andright (with different layouts for the left and right narrow cut-outs)and wide cut-outs for the rest. The narrow cut-out will open out to twoflow ducts laterally (1×2 or 2×2 configuration) while the wide cut-outwill open out to four flow ducts (1×4 configuration) (FIG. 24/31 andFIG. 25/31). The narrow cut-outs exist in two configurations, namely thelarge narrow cut-out and the small narrow cut-out (FIG. 25/31). Thelarge narrow cut-outs can open out to four flow ducts (2×2configuration), while the small narrow cut-outs can open Out to two flowducts (1×2 configuration). The back rubber sheet has only wide cut-outsthroughout (FIG. 26/31 and FIG. 27/31). This arrangement of cut-outswill facilitate the directional change of the coolant flow (FIG. 28/31to FIG. 31/31). The rubber sheets also have the function of sealing thespace between flow ducts.

The novel structure of the apparatus, having a cooling grid array, afront cover with a front rubber sheet having a special cut-out patternand a back cover with a back rubber sheet having a special cut-outpattern, is what allows the coolant to flow in a path that results ineven and effective cooling throughout the apparatus, at the same timekeeping the apparatus compact and lightweight.

Friction Stir Weld (FSW), or any other suitable connection method, canbe used for these connections:

-   -   Front cover with front cooling duct end plate (must be a        leak-proof joint)    -   Back cover with back cooling duct end plate (must be a        leak-proof joint)    -   Bottom plate (FIG. 15/31) with front & back cooling duct end        plate    -   Two side plates (FIG. 16/31) with front & back cooling duct end        plate and bottom plate.

The construction of the final empty battery box is shown in FIG. 17/31.

After the 2S-cells have been inserted in the spaces between the coolingduct plates (FIG. 18/31), with the laying of necessary insulation sheetsand spacers and the connection of the small, big and end clips (asdescribed above), battery management system (BMS) connections and cablescan be laid.

The top cover (FIG. 21/31) has slots that can accommodate a BMS. It isalso equipped with various sockets like a 12V DC connection for the BMS,a main power socket and two Can-bus 2.0 terminals. It also can beequipped with a quick-release coolant connector at the coolant inlet andoutlet. All these make it easy for plug-and-play operation with any EV.

With a top rubber seal (FIG. 18/31) between the top cover and thebattery box secured by fasteners, the entire battery pack box (FIG.22/31) will be an IP65-rated enclosure, suitable for EV application.

FIG. 23/31 shows the schematic flow of the coolant in the cooling gridarray in the battery pack. For simplification, the single cylindricalpipe-like structure represents the path of two flow ducts. The locationsof the flow ducts are depicted in FIG. 24/31 to FIG. 27/31. With theconnection of both the front and back cover with their respective rubbersheets, the flow of the coolant will be able to change direction at therubber sheet cut-out space. How the front rubber sheet is able to changethe flow direction is depicted in FIG. 29/31, and how the back rubbersheet is able to change direction is depicted in FIG. 30/31. FIG. 31/31shows the flow direction at the bottom flow duct layer.

CONCLUSION

This apparatus is able to carry coolant to each individual cell evenly,effectively and efficiently in a simple design, extending the lifespanof the battery and enhancing its safety.

The total weight of the battery pack (FIG. 22/31), including ˜13 kg ofcoolant, is 350 kg.

Its dimensions are L=1031 mm, W=509 mm, H=445 mm.

The battery pack is lightweight but strong, with a voltage of 320V,energy capacity of 32 kWh, energy to weight ratio of ˜91 Wh/kg, and anenergy to volume ratio of ˜137 Wh/L. These specifications will be ableto meet requirements in most EV applications.

Possible Future Implementations

The present-day EV battery packs are produced by the various carmakersin a variety of forms. This results in higher costs from a lack ofeconomies of scale, and no interchangeability of batteries between carsfrom different manufacturers.

If battery packs were standardized, it would be able to be easilyadapted to fit different vehicles. The state grid can possibly produce astandardized battery pack rather than the carmakers themselves, andthere are benefits to be reaped in a number of ways.

Centralized facilities for producing, charging and maintaining batterypacks will result in economies of scale, giving cost savings to bothconsumers and producers. Battery packs can be charged at power stationsduring off-peak hours and delivered to petrol kiosks. In place offilling up petrol, consumers can merely replace their batteries atpetrol kiosks, leaving their flat batteries to be picked up and chargedby the state grid. This will also extend the range of EVs.

With a central charging facility delivering fully-charged battery packsto petrol kiosks, governments need not spend money to build chargingstations at different locations, resulting in substantial savings. Also,consumers need not worry about the serviceability and maintenance oftheir batteries, as the state grid will handle these.

This approach will reduce the price of EVs dramatically and hencepromote market growth. Carmakers only need to design future cars to beable to accommodate a standard battery pack.

The concept and structure of this power battery pack cooling apparatuscan also apply to other future implementations and applicationsrequiring compact and lightweight battery packs, or applicationsrequiring effective cooling systems under space constraints.

1. A power battery pack cooling apparatus, comprising: a cooling gridarray where heat exchange take place, a front cover (having a coolinginlet and outlet which enables the coolant to flow into and out of thecooling apparatus) with an attached front rubber sheet which facilitatesthe flow and the change of direction of the coolant through the spacescreated by the cut-outs, a back cover with an attached back rubber sheetwhich facilitates the flow and the change of direction of the coolantthrough the spaces created by the cut-outs.
 2. A clip system forelectrical connectivity between battery cells, comprising: big clipswhich provide electrical connectivity between two 2S-cells acrosscooling duct plates, small clips which provide electrical connectivitywithin a single 2S-cell between the two battery cells, end clips whichare attached to the positive terminal of the first 2S-cell and thenegative terminal of the last 2S-cell for connection to main powercables.